The myelin proteolipid protein (PLP) is a well characterized CNS myelin protein, which constitutes 50% of the myelin membrane (Eng et al. 1968; Norton and Poduslo, 1973). However, it is expressed also in embryos, neurons and other nonmyelinating cells. Why is this? The current studies focus on the hypothesis that this protein has an additional role that impacts signaling in cells. We hypothesize that PLP interacts with integrins and neurotransmitter receptors, and thereby modulates a series of events in developing brain as well as in the mature brain. This hypothesis derives from studies supported by this grant during the past funding period, in which we demonstrated a direct interaction of PLP with v integrin and the formation of a complex of PLP with av integrin and neurotransmitter receptors in oligodendrocyte progenitor cells, which modulates their interaction with the extracellular matrix (Gudz et al. 2002; 2006). In the proposed studies, we will test the hypothesis that PLP interaction with integrins and neurotransmitter receptors in embryonic and early postnatal development modulates oligodendrocyte and neuron development. In order to investigate this hypothesis, we will pursue the following aims. In aim 1, we will identify the proteins in the PLP signaling complex and the signaling pathways involved. In aim 2, we will investigate the role of the specific proteins in the PLP/integrin/ neurotransmitter receptor complex that mediates oligodendrocyte progenitor cell migration in cultured oligodendrocytes. In aim 3, we will investigate the role of the specific proteins in the PLP/integrin/neurotransmitter receptor modulation of neuron and oligodendrocyte progenitor cell migration in vivo. We will analyze Plp-null, v integrin null and GluR2-null mice, after crossing our Plp-Enhanced Green Fluorescent Protein (EGFP) transgene into them. For some studies we will analyze a conditional knockout mouse that selectively ablates the av integrin in oligodendrocyte progenitor cells in the developing brain. In the final aim, we will analyze the consequences of these null mutations for migration of neurons and oligodendrocyte progenitor cells in cerebellum, optic nerve and embryonic telencephalon, using real time imaging. PUBLIC HEALTH RELEVANCE: The myelin proteolipid protein (PLP) makes up 50% of the protein in the myelin membrane in the central nervous system. However, it is also expressed in embryos, neurons and other nonmyelinating cells. The current studies investigate the hypothesis that in addition to its apparent structural role in myelin, this protein is also involved in cell signaling, which influences how the oligodendrocyte progenitors and immature neurons migrate in the developing nervous system. We have published studies that demonstrate that PLP interacts with integrins, which are cell surface proteins that influence cell-cell and cell-substrate contact. PLP also interacts with neurotransmitter receptors on the surface of oligodendrocyte progenitor cells, which respond to neurotransmitters. The presence of neurotransmitters in the developing nervous system may influence both oligodendrocytes and neurons as they develop, and the fact the PLP and integrins and neurotransmitter receptors interact and change the way the oligodendrocyte progenitor cells migrate is important for normal brain development. In order to investigate our hypothesis, we will pursue the following studies. We will identify other proteins that are involved in this complex and investigate the signaling pathways that these proteins use to modulate oligodendrocyte progenitor cell and immature neuron migration. We will delete PLP, integrin or the neurotransmitter receptor from oligodendrocytes, and investigate how this impacts oligodendrocyte progenitor migration in culture. We will then study animals that have had these proteins selectively deleted, to learn how oligodendrocyte progenitor cells or immature neurons migrate in the developing nervous system, in embryos, in the developing cerebellum and in the developing optic nerve. These studies will have impact for a number of developmental human diseases and will provide insight into how to induce remyelination in adults, in demyelinating diseases such as multiple sclerosis.